<template>
  <ul class="list">
    <li class="item" 
        v-for="(item, index) in letters" 
        :key="index"
        :ref="item"
        @touchstart.prevent="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        @click="handleLetterClick"
    >
        {{item}}</li>
  </ul>
</template>
<script>
export default {
  props: {
    'keys': Array
  },
  data () {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    }
  },
  updated() {
    this.startY = this.$refs['A'][0].offsetTop
  },
  computed: {
    letters () {
      const letter = []
      this.keys.forEach(element => {
        letter.push(element)
      })
      return letter
    }
  },
  methods: {
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      // 函数截流
      if (this.timer) {
        clearTimeout(this.timer)
      }
      this.timer = setTimeout(() => {
        if(this.touchStatus){
          // const startY = this.$refs['A'][0].offsetTop
          const touchY = e.touches[0].clientY - 79
          const index = Math.floor((touchY - this.startY) / 20)
          
          if (index >= 0 && index < this.letters.length) {
            this.$emit('change',this.letters[index])
          }
        }
      }, 16)
      // if(this.touchStatus){
      //   // const startY = this.$refs['A'][0].offsetTop
      //   const touchY = e.touches[0].clientY - 79
      //   const index = Math.floor((touchY - this.startY) / 20)
        
      //   if (index >= 0 && index < this.letters.length) {
      //     this.$emit('change',this.letters[index])
      //   }
      // }
    },
    handleTouchEnd () {
      this.touchStatus = false
    },
    handleLetterClick (e) {
      this.$emit('change',e.target.innerText)
      
    }
  }
}
</script>
<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
  .list
    display flex
    flex-direction column
    justify-content center
    position absolute
    top 1.58rem
    right 0
    bottom 0
    width .4rem
    .item
      line-height .4rem
      text-align center
      color $bgColor
</style>
